.validate() doesn't test un-saved fields of a retrieved model

If I set properties via the set method on a model, they don't get picked up immediately for validation. To workaround this, I'm creating a dummy model that I don't save with the same properties. This shouldn't be necessary.

I likely won't test this until the final release, or the first patch after, given my experience trying to port to PR3, but if this is still in issue an whatever release I eventually migrate to, my automated tests will catch it and I'll re-file a report.

I feel good that you couldn't reproduce the problem in the beta, though. This gives me hope for a smoother migration next time!